The present invention relates to a fuel injector for injecting atomized fuel to an engine, and more particularly to an improvement in atomization of the fuel to be injected from such a fuel injector to the engine.
FIG. 18 shows a front portion of a conventional fuel injector most pertinent to the present invention. Referring to FIG. 18, reference numeral 101 designates a casing of the injector for fixedly mounting a valve housing 102 therein. The valve housing 102 is formed at its front end with a nozzle 103 for injecting fuel and a valve seat 104 continuing inwardly from the nozzle 103. A valve body 105 is reciprocatably mounted in the valve housing 102. A spherical valve member 105a adapted to contact the valve seat 104 is fixed to a front end of the valve body 105. When the valve body 105 is moved upwardly as viewed in FIG. 18, a gap is defined between the valve seat 104 and the valve member 105a to permit pass of the fuel therethrough and inject the fuel from the nozzle 103.
A cylindrical adapter 106 is fixed to a front end portion of the valve housing 102. The adapter 106 is formed with an atomizer hole 107 communicating with the nozzle 103. The adapter 106 is further formed with a plurality of assist air passages 108 extending through a side wall of the adapter 106 for supplying an assist air into the atomizer hole 107, so as to atomize the fuel injected from the nozzle 103 into the atomizer hole 107.
While the spherical valve member 105a is shown in FIG. 18 by way of example, a pintle-type valve member having a needle partially inserted into the nozzle is also known.
In the prior art injector having the spherical valve member or the pintle-type valve member, the fuel injected from the nozzle 103 is not straightened or not in a columnar shape. Accordingly, the correlation in flow between the injected fuel and the assist air colliding with the same does not become constant, and a spray contour of the atomized fuel becomes unstable.
As a result, the atomized fuel is partially deposited onto an inner wall of the adapter 106, and the deposited fuel is further coagulated to form fuel drops 109. Admission of such fuel drops 109 into an engine makes unstable an air-fuel ratio of a fuel mixture to be supplied to the engine, causing a fluctuation in engine speed.
Further, as the spray contour of the atomized fuel is unstable, the atomized fuel injected from the atomizer hole 107 is deposited onto an inner wall of a suction pipe mounting the injector thereto, which also causes the fluctuation in air-fuel ratio.
Further, as the correlation in flow between the injected fuel and the assist air is not constant, the atomization of the injected fuel by the assist air becomes non-uniform to cause a variation in particle size of the atomized fuel, resulting in a reduction in combustion efficiency of the atomized fuel in the engine.